Ive got a metal shed on a roof of an apartment in Japan that needs to be insulated. The walls are hollow between the exterior metal wall and the interior dry wall. I havent been able to check under the roof of the shed yet.

Since the whole property is a rental, Im not interested in any solutions which might be expensive (ie suitable for long-term owners). Something quick, cheap, and reasonably effective for heat insulation-was thinking about pouring styrofoam peanuts down inside the wall hollows.

Would much appreciate any ideas yall might have. & If you ever come to Kobe, Im buying the beer.